Such high temperature ovens in the form of vacuum furnaces are used for firing objects which have to be fired in successive oven zones in different gas atmospheres, partly at very low gas pressures. In such high temperature ovens, temperatures of up to 1800° C. may prevail during the firing process.
Firing material exists which is fired in a first oven zone in a first gas atmosphere and subsequently has to be passed through a second oven zone in which it may be fired in a second, different gas atmosphere. During the firing process, in which different gas atmospheres prevail in the successive oven zones, said two oven zones are separated from one another in a gas-tight manner by the gate panel of a gate unit mentioned in the introduction.
In known gate units, for example, a silicone seal is used as a sealing element which has a temperature resistance of 240° C., up to a maximum of 300° C. If firing material has to be transferred from one oven zone into the next, the two oven zones adjacent to one another have to be evacuated first so that it does not result in an undesirable mixing of gases when the gate panel is opened. Optionally, the oven zones may be flooded with an inert gas before the gate panel is opened.
Irrespective of whether the gate unit is used in a vacuum furnace or not, the two oven zones adjacent to one another have to be brought to the same pressure level before the gate panel is opened. Even with an oven which is not operated at low pressure, in which two oven zones adjacent to one another are flooded with different operating gases during the firing process, said two oven zones enclosing a sluice chamber have to be evacuated before the gate panel is opened; the pressure then has to be equalised, for which the oven zones may optionally be filled with an inert gas.
If the gate panel is now moved into its open position in order to open up the path between the two oven zones adjacent to one another, at least one segment of the seal passes through the hot oven tunnel.
So that this segment of the seal is not subjected to any radiant heat which is harmful thereto, the temperature in the oven tunnel of known high temperature ovens is reduced in advance to a temperature at which the silicone seal does not sustain damage. Thus, for example, temperatures of up to 550° C. are possible if the silicone seal is only briefly subjected to this temperature, which is the case when raising or lowering the gate panel.
After transferring the firing material from the first oven zone into the second oven zone, the gate panel is closed again and the oven accordingly has to be heated up again to its operating temperature of 1500° C. to 1800° C.
By lowering the temperature and the subsequent heating-up, the process of transferring firing material from one oven zone to the next is relatively lengthy and also consumes a correspondingly high amount of energy.
The present invention is directed to resolving these and other matters.